Answer: First of all, Mazal Tov on the upcoming Simcha.
If there will not be enough time to buy them afterwards, they may even be purchased during the week of Tisha b'Av, as per the Rema. The same would apply to the dry cleaners, though I would suspect that there is enough time during the two weeks after Tisha b'Av, in which case there is no Heter.
Even if the issue is only saving money, the Mishna Berura writes that this too is sufficient grounds to permit purchasing items.